Degradation Of Cylindrospermopsin Research Articles

Biodegradation of cylindrospermopsin toxin by microcystin-degrading bacteria isolated from cyanobacterial blooms

Cylindrospermopsin (CYN) is highly water soluble and stable cyanotoxin which can persist in water sources and pose health hazards to human, animals and plants. Consequently, there is a need to fully understand the fate of CYN in the aquatic environment, in particular, its biodegradation by endemic organisms. Although there is evidence of CYN degradation by microbial population, bacterial strains responsible for the toxin degradation are not yet identified. This study reports for the first time CYN degradation by Bacillus strain (AMRI-03) isolated from cyanobacterial blooms. In degradation batch experiment, the strain grew well in the presence of CYN without showing any lag period, and this growth increased with the initial CYN concentration. CYN degradation occurred rapidly, and the complete degradation was dependent on the initial CYN concentration. It occurred after 6 days at the highest concentration (300 μg L−1) compared to 7 and 8 days at lower concentrations (10 & 100 μg L−1). Also, the degradation rate correlated positively with the initial CYN concentration with maximum value (50 μg L−1 day−1) obtained at the highest CYN concentration. Furthermore, the biodegradation rate of CYN by this strain depended remarkably on temperature and pH. The highest biodegradation rates were obtained at 25 and 30 °C, and at pH 7 and pH 8. Taken that such microcystin-degrading strain can also degrade CYN, bacterial strains reported worldwide as microcystin degraders could be tested for their capability of CYN degradation.

Cylindrospermopsin degradation in sediments – The role of temperature, redox conditions, and dissolved organic carbon

One possible consequence of increasing water temperatures due to global warming in middle Europe is the proliferation of cylindrospermopsin-producing species from warmer regions. This may lead to more frequent and increased cylindrospermopsin (CYN) concentrations in surface waters. Hence, efficient elimination of CYN is important where contaminated surface waters are used as a resource for drinking water production via sediment passage. Sediments are often characterized by a lack of oxygen and low temperature (i.e. approx. 10°C). The presence of dissolved organic carbon (DOC) is not only known to enhance but also to retard contaminant degradation by influencing the extent of lag phases. So far CYN degradation has only been investigated under oxic conditions and at room temperature. Therefore, the aim of our experiments was to understand CYN degradation, focusing on the effects of i) anoxic conditions, ii) low temperature (i.e. 10°C) in comparison to room temperature (23±4°C) and iii) DOC on lag phases. We used two natural sandy sediments (virgin and preconditioned) and surface water to conduct closed-loop column experiments. Anoxic conditions either inhibited CYN degradation completely or retarded CYN breakdown in comparison to oxic conditions (T1/2 (oxic)=2.4 days, T1/2 (anoxic)=23.6 days). A decrease in temperature from 20°C to 10°C slowed down degradation rates by a factor of 10. The presence of DOC shortened lag phases in virgin sediments at room temperature but induced a lag phase in preconditioned sediments at 10°C, indicating potential substrate competition. These results show that information on physico-chemical conditions in sediments is crucial to assess the risk of CYN breakthrough.

Retention and degradation of the cyanobacterial toxin cylindrospermopsin in sediments – The role of sediment preconditioning and DOM composition

Recent results show that cylindrospermopsin is more frequent and widespread in surface waters than previously assumed. Studies on the fate of CYN in sediments are lacking, but this is important if these resources are used for drinking-water production via sediment passage. Therefore, the aim of our study was to determine a) CYN retention in two sandy sediments as a function of flow rate, CYN concentration, the presence of DOM and the content of fines (1% and 4%, respectively) and b) the influence of sediment preconditioning and DOM composition of the water (aquatic DOM versus DOM released from lysed cells) on CYN degradation. Retention of CYN proved negligible under the investigated conditions. Degradation in virgin sediments showed the highest lag phases (20 days). Preconditioned sediments showed no lag phase. The presence of aquatic DOM yielded highest degradation rates ( κ 1 = 0.46 and 0.49 day −1) without a lag phase. Readily available organic carbon sources were preferentially metabolized and hence induced a lag phase. Thus, the presence and composition of DOM in the water proved important for both CYN degradation rates in preconditioned sediments and for the lag phase. Cylindrospermopsin degradation took place solely in the sediment and not in the water body.

Cylindrospermopsin is not degraded by co-occurring natural bacterial communities during a 40-day study

Biodegradation of cylindrospermopsin produced by Aphanizomenon ovalisporum UAM 290 was studied. In the 40-day degradation experiment conducted, bacterial communities from two waterbodies with and without previous exposure to the toxin were used. Further, and in order to study the potential effect of other organic substrates on the degradation of cylindrospermopsin, three different sources of cylindrospermopsin were used: toxic extracts obtained by methanolic extraction and by ultrasonication in water with 5% formic acid and 0.9% NaCl and toxin naturally present in the spent media of an Aphanizomenon ovalisporum culture. Despite active growth of the bacterial population and consumption of DOC in presence of the toxic extracts, no degradation of cylindrospermopsin could be observed during the 40-day period. Considering that cylindrospermopsin is abundant in the extracellular fraction and that photodegradation in the field seems to be limited, a lack of efficient biodegradation as observed in our study could be of greatest importance and further explain the accumulation of this toxin in the dissolved fraction of the waterbodies investigated.

Kinetics of the oxidation of cylindrospermopsin and anatoxin-a with chlorine, monochloramine and permanganate

Cyanobacteria produce toxins that may contaminate drinking water sources. Among others, the presence of the alkaloid toxins cylindrospermopsin (CYN) and anatoxin-a (ANTX) constitutes a considerable threat to human health due to the acute and chronic toxicity of these compounds. In the present study, not previously reported second-order rate constants for the reactions of CYN and ANTX with chlorine and monochloramine and of CYN with potassium permanganate were determined and the influence of pH and temperature was established for the most reactive cases. It was found that the reactivity of CYN with chlorine presents a maximum at pH 7 (rate constant of 1265 M −1 s −1). However, the oxidation of CYN with chloramine and permanganate are rather slow processes, with rate constants <1 M −1 s −1. The first chlorination product of CYN was found to be 5-chloro-CYN (5-Cl-CYN), which reacts with chlorine 10–20 times slower than the parent compound. The reactivity of ANTX with chlorine and chloramines is also very low (k<1 M −1 s −1). The elimination of CYN and ANTX in surface water was also investigated. A chlorine dose of 1.5 mg l −1 was enough to oxidize CYN almost completely. However, 3 mg l −1 of chlorine was able to remove only 8% of ANTX, leading to a total formation of trihalomethanes (TTHM) at a concentration of 150 μg l −1. Therefore, chlorination is a feasible option for CYN degradation during oxidation and disinfection processes but not for ANTX removal. The permanganate dose required for CYN oxidation is very high and not applicable in waterworks.

Photocatalytic Degradation of the Cyanotoxin Cylindrospermopsin, using Titanium Dioxide and UV Irradiation

Cylindrospermopsis raciborskii produces the cyanotoxin cylindrospermopsin, which is commonly found in SouthEast Queensland water reservoirs, and has been responsible for the closure of these reservoirs as a source of drinking water in recent times. Thus, alternative more effective treatment methods need to be investigated for the removal of toxins such as cylindrospermopsin. This study examined the effectiveness of two brands of titanium dioxide under UV photolysis for the degradation of cylindrospermopsin. Results indicate that titanium dioxide is an efficient photocatalyst for cylindrospermopsin degradation. The titanium dioxide (TiO 2), brand Degussa P-25 was found to be more efficient than the alternate brand Hombikat UV-100. There was an influence from solution pH (4, 7, and 9) with both brands of titanium dioxide, with high pH resulting in the best degradation rate. Importantly, there was no adsorption of cylindrospermopsin to titanium dioxide particles as seen with other cyanotoxins, which would adversely influence the degradation rate. Degradation rates were not influenced by temperature (19–34°C) when P-25 was the source of TiO 2, some temperature influence was observed with UV-100. Dissolved organic carbon concentration will reduce the efficiency of titanium dioxide for cylindrospermopsin degradation, however the presence of other inorganic matter in natural waters greatly assists the photocatalytic process. With minimal potentially toxic by-product formation expected with this treatment, and the effective degradation of cylindrospermopsin, titanium dioxide UV photolysis is a promising speculative alternative water treatment method.

Degradation of the cyanobacterial toxin cylindrospermopsin, from Cylindrospermopsis raciborskii, by chlorination

Cylindrospermopsin, a potent cyanobacterial toxin produced by Cylindrospermopsis raciborskii and other cyanobacteria, is regularly found in water supplies of Queensland, Australia. This study focussed on the effectiveness of chlorination as a water treatment procedure for cylindrospermopsin degradation. The results demonstrate that relatively low chlorine doses (<1 mg l −1) are sufficient for degradation of cylindrospermopsin, when the dissolved organic carbon content is low. However, if organic matter other than cylindrospermopsin is present in the solution, the effectiveness of chlorine for cylindrospermopsin degradation is reduced as other organic matter present consumes chlorine. Under the experimental conditions using samples with a solution pH of 6–9, a residual chlorine concentration of 0.5 mg l −1 was sufficient to degrade >99% of cylindrospermopsin. Toxin degradation via chlorination occurs within the first minute and no difference was observable between degradation in an open system and in a closed system. With a decrease of the pH from 6 to 4 a reduction in the efficiency of chlorine for degradation of cylindrospermopsin was observable, a possible indication that cylindrospermopsin is more stable to chlorine degradation at lower pH. However, in normal water treatment this is not relevant since the pH is consistently higher than 6.

Stability of cylindrospermopsin, the toxin from the cyanobacterium,Cylindrospermopsis raciborskii: Effect of pH, temperature, and sunlight on decomposition

Cylindrospermopsin is a powerful hepatotoxin produced by the cyanobacterium Cylindrospermopsis raciborskii. It is considered a potential threat to livestock, wildlife, and humans, and is the suspected cause of an outbreak of hepatoenteritis on Palm Island, Queensland, Australia, and various stock poisoning incidents around Australia. In this study, the stability of cylindrospermopsin was investigated using different parameters, including visible and UV light, sunlight, temperature and pH. Cylindrospermopsin decomposes rapidly (half-life of 1.5 h) when exposed to sunlight in an algal extract solution; however, no decomposition was recorded in pure cylindrospermopsin and Milli-Q water solutions. Cylindrospermopsin decomposes slowly in temperatures ranging from 4 to 50°C at pH 7. After 10 weeks at 50°C, cylindrospermopsin had degraded to 57% of the original concentration. This degradation was accompanied by an increase in another compound which is believed to be structurally related to cylindrospermopsin. Boiling does not cause a significant degradation of cylindrospermopsin within 15 min. Initial investigations indicate that cylindrospermopsin is degraded slowly under artificial light ranging from 42, 29, and 9 μE m−1 s−1 and in darkness. Degradation of cylindrospermopsin was not affected by changes in pH. Experiments were performed in sterile conditions. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 155–161, 1999